Although vaccination is the first-line strategy controlling and preventing influenza A/H1N1 for older adults, personal protective measures, such as wearing facemasks, are also important preventive behaviors to reduce the risk of becoming infected with influenza A/H1N1 during a pandemic. In the current study, we aimed to explore the belief-related psychological factors of wearing facemasks for influenza A/H1N1 prevention in a sample of Hong Kong older adults. Community-dwelling Chinese adults (N = 137) aged between 65 and 80 years (Mage = 75.10; SDage = 6.49) participated in semistructured interviews. Data were analyzed using theoretical thematic analysis and identified themes were matched deductively within the belief-based processes of the health belief model. Results revealed beliefs that underpinned 4 general dimensions of facemask wearing: (1) perceived susceptibility and seriousness of influenza A/H1N1 pandemic (e.g., influenza A/H1N1 as contagious and lethal), (2) modifying factors (e.g., social responsibility to prevent influenza), (3) cues to action (e.g., seeing others doing it), and (4) perceived benefits and barriers (e.g., protects oneself and others, difficult to breathe). Future interventions can target these beliefs to improve facemask wearing of older adults and, thus, curb preventable infection rates during an influenza A/H1N1 pandemic.